A negative air ion is an atom or molecule in the air that has gained an electron, while a positive ion has lost an electron. Both positive and negative ions occur naturally in the air. However, negative ions are more concentrated in fresh air. Negative air ions can be produced by lightning, ocean surf and waterfalls. There are also electrical devices called 'air ionisers' that produce negative air ions. Such air ionisers have been used in the treatment of seasonal winter depression, or seasonal affective disorder (SAD). Treatment generally involves sitting in a room with the ioniser on for 30 minutes every morning over a 2-3 week period.
Negative air ionisation is mainly used for people who tend to become depressed in autumn and winter, when the daylight is shorter. These people then get better in spring and summer. This type of depression is known as seasonal affective disorder (SAD). It is unclear how negative air ions might improve mood, and more research is needed to better understand how it might work.
There have been a number of small studies which have looked at the effects of air ionisation on winter depression. One meta-analysis which looked at the results from five studies found that high density air ionisation was effective at helping people with both SAD and non-seasonal clinical depression, while low density air ionisation was only effective for people with SAD.
Most of the research looking at negative air ionisation for depression has focussed on people with seasonal depression. More research is needed to better understand if negative air ionisation is helpful for people with non-seasonal depression.
Some air ionisers produce a very small amount of a gas called ozone, which can be harmful to humans. Air ionisers should be used in a well ventilated room to ensure that ozone levels do not build up to toxic levels.
Air ionisers are available from electronics stores and can be bought on the internet. It is important to check the technical specifications of any air ioniser to see if they produce a high density of negative ions.
Air ionisation appears to be an effective treatment for seasonal winter depression, but it is recommended that other better supported treatments such as light therapy are tried first. More research is needed to understand if air ionisation could be helpful for non-seasonal depression.
Last reviewed and updated: 1 November 2019